SYNTHESIS AND STRUCTURE OF AS-PREPARED ITQ-4, A LARGE-PORE PURE SILICA ZEOLITE - THE ROLE AND LOCATION OF FLUORIDE ANIONS AND ORGANIC CATIONS

Pure silica ITQ-4, a zeolitic material with large one-dimensional 12MR channels and an unexpectedly large microporous void volume, can be sy nthesized in the presence of fluoride ions and N-benzylquinuclidinium cations within a wide range of synthesis pH. Substitution of the terti ary carbon of the quinuclidine moiety by a N atom still renders the or ganic cation as a suitable structure-directing agent for this material . The role of F- anions and the influence of the pH of the synthesis o n both the phase selectivity of the crystallization and the presence o f connectivity defects in the final material are discussed. In the pre sence of F-, defect formation is observed to be pH-dependent, and ther e appears to be a threshold pH for the generation of a constant defect concentration. A plausible explanation for this observation based upo n the ionization state of the condensing species is also presented. Th e structure of as-made ITQ-4 has been obtained and refined from high-r esolution powder XRD data, and the organic and fluoride ions have been located. The sinuosity of the channel of ITQ-4 is found to coincide w ith the bent geometry observed for the structure-directing agent, whil e the fluoride ions are found to reside within a small [4(3)5(2)6] cag e located around the periphery of the central pore space.